1. Field of the Invention
This invention relates to a support device for a rocker arm used as a component of a valve mechanism for actuating an engine valve of an internal combustion engine.
2. Description of the Prior Art
A rocker arm of the above-mentioned kind has been conventionally proposed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 2000-303806, which includes a rocker shaft supported between a pair of supporting portions formed in a cylinder head, and a rocker arm pivotally movably supported on the rocker shaft via its supported portion. Further, a wave washer is mounted on one end of the supported portion of the rocker arm. The wave washer is comprised of a resilient annular portion bent in an outwardly curved manner, and a pair of engaging pieces extending inward from diametrically opposite portions of the annular portion. Each engaging piece has a predetermined bent shape and is resilient. On the other hand, the supported portion of the rocker arm has a pair of engaging holes formed at respective locations corresponding to the pair of engaging pieces. The wave washer has its engaging pieces precisely fitted in the engaging holes, respectively, and sandwich the supported portion of the rocker arm from opposite sides by the resilience of the engaging pieces, whereby the wave washer is unrotatably held on the supported portion of the rocker arm. The rocker shaft is inserted through the supported portion of the rocker arm and the annular portion of the wave washer, and in the assembled state of these members, the wave washer is sandwiched between the supported portion of the rocker arm and one of the aforementioned supporting portions, and the annular portion urges the rocker arm by the resilience thereof toward the other of the supporting portions, whereby the rattling of the rocker arm in the thrust direction is prevented.
In the conventional support device for the rocker arm, however, in assembling the wave washer to the rocker arm, it is necessary to circumferentially align the pair of engaging pieces of the wave washer with the pair of engaging holes of the rocker arm, respectively, which degrades the working efficiency in assembling the wave washer to the rocker arm. Further, since the engaging pieces of the wave washer are engaged with the engaging holes of the rocker arm, the wave washer is unrotatable with respect to the rocker arm, and further, since the wave washer is sandwiched between the rocker arm and the one of the supporting portions by the reactionary force of its own resilience, the rotation thereof is restricted. Therefore, as the rocker arm is pivotally moved, part of large load acting from the cam and the valve spring on the rocker arm acts on the wave washer. This makes the wave washer, particularly the engaging pieces, susceptible to deformation or wear. Further, since the supported portion of the rocker arm receiving large load from the cam and the valve spring is formed with the engaging holes, the resulting decrease in the cross-sectional area of the supported portion lowers the rigidity and strength of the supported portion.
It is an object of the invention to provide a support device for a rocker arm, which is capable of suppressing deformation or wear of a washer, and greatly improving the working efficiency in assembling the washer to the rocker arm.
To attain the above object, the invention provides a support device for supporting a rocker arm that includes a supported portion and actuates an engine valve of an internal combustion engine having a cylinder head,
the support device comprising:
a plurality of shaft holders arranged in the cylinder head;
a rocker shaft supported by the plurality of shaft holders, for supporting the rocker arm thereon via the supported portion of the rocker arm between a pair of the shaft holders, such that the rocker arm can pivotally move thereabout; and
a washer attached to one of respective opposed ends of the supported portion of the rocker arm and one of the shaft holders, in a manner interposed between the one of the opposed ends and the other of the opposed ends, the washer having an engaging piece,
wherein the one of the opposed ends is formed with an annular engaging portion for having the washer engaged thereon via the engaging piece.
According to this support device for a rocker arm, a washer is attached to one of respective opposed ends of a supported portion of the rocker arm and one of shaft holders, in a manner interposed between the opposed ends. Further, the washer has an engaging piece, and the one of the opposed ends to which the washer is attached is formed with an annular engaging portion. The washer is latched or engaged on the supported portion of the rocker arm or the shaft holder by the engagement between the engaging piece and the annular engaging portion. Thus, the engaging piece of the washer is engaged with the annular engaging portion, which enables the washer to be assembled to the rocker arm or the shaft holder at any relative rotational angle thereto. This makes it absolutely unnecessary to carry out an operation for aligning the engaging piece with an engaging hole, which has been conventionally necessary, thereby greatly improving the working efficiency in assembling the washer to the associated component.
Preferably, the washer is engaged with the annular engaging portion via the engaging piece in a manner rotatable relative to the annular engaging portion.
According to this preferred embodiment, the rotation of the washer relative to the rocker arm or the shaft holder is permitted, whereby load applied from a cam or a valve spring via the rocker arm to the washer becomes very small, which makes it possible to suppress deformation or wear of the washer.
Preferably, the engaging piece comprises a plurality of engaging pieces arranged at intervals along a circumference of the washer, and the annular engaging portion is configured to be continuous along a circumference of the one of the opposed ends.
According to this preferred embodiment, the engaging piece of the washer comprises a plurality of engaging pieces circumferentially arranged, while the annular engaging portion is configured to be circumferentially continuous. This makes it possible to engage the plurality of engaging pieces on the annular engaging portion at any relative rotational angle without requiring any aligning work, and thereby maintain excellent working efficiency in assembling the washer to the rocker arm or the shaft holder. Further, since the engaging piece comprises a plurality of the engaging pieces, compared with a case in which the engaging piece is circumferentially continuous, it is easy to deform the engaging pieces, which further enhances working efficiency in assembling the washer to the rocker arm or the shaft holder. Moreover, when the washer is attached to the one of the opposed ends in a manner relatively rotatable, it is possible to reduce the rotational resistance of the washer.
Preferably, the annular engaging portion is formed by an annular protruding portion.
The supported portion of the rocker arm and the shaft holder are portions receiving large load from a cam or a valve spring when the rocker arm is pivotally moved, and therefore, it is preferred that they are configured to have as much rigidity and strength as possible. According to this preferred embodiment, the annular engaging portion for having the washer engaged thereon is configured as an annular protruding portion, and therefore, the resulting increase in cross-sectional area of the supported portion of the rocker arm or the shaft holder can make the rigidity and strength thereof much larger than in the case of the prior art in which engaging holes are formed therein.
Preferably, the washer is attached to the supported portion of the rocker arm, and at least part of the engaging piece is orthogonal to an axis of the rocker arm, and at the same time arranged at a location closer to a center of the supported portion than a plane passing on an outer end of an abutment portion of the rocker arm where the rocker arm is in abutment with the engine valve.
According to this preferred embodiment, at least part of the engaging piece is arranged by making effective use of space inside (not outward of) an abutment portion of the rocker arm where the rocker arm is in abutment with the engine valve. Therefore, the rocker arm can be made compact in size.
Preferably, the washer is attached to an end of the one of the shaft holders opposed to the rocker arm out of the respective opposed ends of the supported portion of the rocker arm and one of the shaft holders, and the annular protruding portion is formed at the end of the one of the shaft holders.
According to this preferred embodiment, since the shaft holder is formed with the annular protruding portion, it is possible to enhance not only the rigidity and strength of the shaft holders, but also the supporting rigidity of the rocker shaft supported by the shaft holders.
Preferably, the supported portion is formed with a projection corresponding to an overflow port used during casting of the rocker arm.
According to this preferred embodiment, the rigidity and strength of the supported portion can be further increased by the projection.
More preferably, the projection is formed on a flat surface of the supported portion radially inwardly offset from other peripheral portions of the supported portion.
According to this preferred embodiment, since the projection is formed on a flat surface of the supported portion radially inwardly offset from other peripheral portions of the supported portion, the engaging piece of the washer is prevented from being caught on the projection, thereby-ensuring rotation of the washer relative to the rocker arum.
Preferably, the washer comprises an annular portion having a central portion formed with a shaft hole through which the rocker shaft extends, and a plurality of the engaging pieces which extend from an outer periphery of the annular portion, and each of the engaging pieces comprises a perpendicular portion shortly extending perpendicularly from the annular portion and a curved portion having a semi-circular shape and extending inwardly from the perpendicular portion.
More preferably, the washer is attached to the supported portion of the rocker arm, and the supported portion has an outer peripheral surface formed with an annular concave portion which is adjacent to the annular protruding portion and with which the curved portion of the engaging piece is engaged.
According to this preferred embodiment, the washer can be stably held on the rocker arm by the engagement of the annular concave portion and the curved portion of the engaging piece.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.